The present invention relates to a pattern formation method, and more particularly, it relates to a method of forming a resist pattern, used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength of a 1 nm through 180 nm band.
Currently, in fabrication of a large capacity semiconductor integrated circuit, typically such as a 64 Mbit dynamic random access memory (DRAM), a logic device or a system LSI with a 0.25 xcexcm through 0.18 xcexcm rule, a resist pattern is formed by using a resist material including a polyhydroxystyrene derivative as a main component and exposing light of KrF excimer laser (with a wavelength of a 248 nm band).
Moreover, in a pattern formation method under development for a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 xcexcm through 0.13 g m rule, ArF excimer laser operated at a shorter wavelength (of a 193 nm band) than the KrF excimer laser is to be used as the exposing light.
A resist material including a polyhydroxystyrene derivative as a main component includes an aromatic ring having a high absorbing property against light of a wavelength of a 193 nm band. Therefore, the exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film made from this resist material, and hence, a good pattern shape cannot be obtained with this exposing light. Accordingly, the resist material including a polyhydroxystyrene derivative as a main component cannot be used when the ArF excimer laser is used as the exposing light.
Therefore, when the ArF excimer laser is used as the exposing light, a material including, as a main component, a polyacrylic acid derivative free from an aromatic ring is used as a resist material.
On the other hand, X-rays and electron beams (EB) are now examined to be used as exposing light in a pattern formation method applicable to higher resolution.
When X-rays are used as the exposing light, however, there arise various problems in an aligner and formation of a mask. Also, when EB is used as the exposing light, there arises a problem of through put, and hence, EB is not suitable to mass production. Thus, X-rays and EB are not preferred as the exposing light.
Accordingly, in order to form a resist pattern finer than 0.13 xcexcm, it is necessary to use, as the exposing light, a laser beam with a wavelength shorter than that of the ArF excimer laser, such as a Xe2 laser beam (with a wavelength of a 172 nm band), a F2 laser beam (with a wavelength of a 157 nm band), a Kr2 laser beam (with a wavelength of a 146 nm band), an ArKr laser beam (with a wavelength of a 134 nm band), an Ar2laser beam (with a wavelength of a 126 nm band) or a soft X-ray beam (with a wavelength of a 13, 11 or 5 nm band).
Therefore, the present inventors have formed a resist pattern from a resist film of a known resist material through pattern exposure using a F2 laser beam (with a wavelength of a 157 nm band).
However, the resultant resist pattern does not have a rectangular sectional shape but has a defective pattern shape.
In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using light of a wavelength of a 1 nm through 180 nm band as exposing light.
The present inventors have earnestly examined the cause of the defective pattern shape of a resist pattern formed by using a conventionally known resist material, specifically, a resist material including a polyhydroxystyrene derivative or a polyacrylic acid derivative as a main component. As a result, it has been found that a carbonyl group included in the polyhydroxystyrene derivative or the polyacrylic acid derivative has a high absorbing property against light of a wavelength of a 1 nm through 180 nm band, so that the exposing light of a wavelength of a 1 nm through 180 nm band cannot sufficiently reach the bottom of the resist film. This seems the cause of the defective pattern shape of the resultant resist pattern.
Chemical Formula A below represents an example of the polyhydroxystyrene derivative used as a positive resist material in using KrF excimer laser, and Chemical Formula B below presents an example of the polyacrylic acid derivative used as a positive resist material in using ArF excimer laser. 
The present inventors have variously studied about means for decreasing the absorbing property of a resist film against light of a wavelength of a 1 nm through 180 nm band. As a result, it has been found that the absorbing property of a resist film against light of a wavelength of a 1 nm through 180 nm band can be decreased when the resist material includes a sulfonic ester.
This is because a sulfonyl group corresponding to a light absorbing portion of a sulfonic ester has a lower absorbing property against light of a wavelength of a 1 nm through 180 nm band than a carbonyl group included in the polyhydroxystyrene derivative or the polyacrylic acid derivative.
The present invention was devised on the basis of the findings, and specifically, the first pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material including a base polymer having a sulfonyl group on a side chain; conducting pattern exposure by irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band; and forming a resist pattern by developing the resist film with a developer after the pattern exposure.
In the first pattern formation method, since the base polymer of the resist material has a sulfonyl group on the side chain, the absorbing property of the resist film against the exposing light of a wavelength of a 1 nm through 180 nm band is decreased. Therefore, the transmittance of the exposing light with a wavelength of a 1 nm through 180 nm band in the resist film is increased, and hence, the exposing light can sufficiently reach the bottom of the resist film. As a result, a resist pattern can be formed in a good pattern shape.
In the first pattern formation method, the base polymer preferably has a sulfonic ester on a side chain.
In this manner, the side chain of the base polymer is cut by the pattern exposure, so that the solubility of the base polymer in the developer can be easily changed.
In the first pattern formation method, the base polymer preferably has sulfonic acid on a side chain.
In this manner, the adhesion of the resist film onto the substrate can be improved as well as the solubility of the resist film in the developer can be controlled.
In the first pattern formation method, the resist material preferably further includes a polymer having sulfonic acid on a side chain.
In this manner, the adhesion of the resist film onto the substrate can be improved as well as the solubility of the resist film in the developer can be controlled.
In the first pattern formation method, the base polymer preferably includes a compound represented by any of the following General Formulas 1 through 5: 
wherein R indicates a sulfonic ester; R1 indicates a hydrogen atom, a hydroxyl group or an alkyl group; R2 and R3 are the same or different and selected from the group consisting of a hydrogen atom and an alkyl group.
In this manner, the base polymer includes an aromatic ring or a cyclic aliphatic group, and hence, the resistance against dry etching can be improved.
In the first pattern formation method, the sulfonic ester is preferably represented by any of the following Chemical Formulas 6 through 11: 
wherein R4 and R5 are the same or different groups selected from the group consisting of an alkyl group and an aryl group; 
In this manner, the absorbing property of the resist film against the exposing light of a wavelength of a 1 nm through 180 nm band can be definitely decreased.
The first pattern formation method preferably further comprises, between the step of conducting pattern exposure and the step of forming a resist pattern, a step of conducting a heat treatment on the resist film.
In this manner, decomposition of the base polymer in an exposed portion of the resist film is accelerated due to a catalytic reaction of sulfonic acid generated from the base polymer through decomposition by the exposing light.
In this case, solubility of the base polymer in the developer preferably changes in the presence of an acid, and the resist material preferably further includes an acid generator for generating an acid through irradiation with the exposing light.
In this manner, sulfonic acid generated from the base polymer through decomposition by the exposing light and the acid generated from the acid generator are heated, so as to accelerate the catalytic reaction of the acids. As a result, the decomposition of the base polymer is further accelerated in the exposed portion of the resist film.
The second pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, a resist material including an alkali-soluble base polymer and an agent for inhibiting dissolution of the base polymer which is made from a compound including a sulfonic ester and decomposes through irradiation with exposing light; conducting pattern exposure by irradiating the resist film with the exposing light of a wavelength of a 1 nm through 180 nm band; and forming a resist pattern by developing the resist film with a developer after the pattern exposure.
In the second pattern formation method, since the resist material includes the agent for inhibiting dissolution of the base polymer made from the compound including a sulfonic ester, the absorbing property of the resist film against the exposing light of a wavelength of a 1 nm through 180 nm band is decreased. Therefore, the transmittance of the exposing light of a wavelength of a 1 nm through 180 nm band in the resist film is increased, and hence, the exposing light can sufficiently reach the bottom of the resist film. As a result, a resist pattern can be formed in a good pattern shape.
In the second pattern formation method, the base polymer is preferably an acrylic type resin, a styrene type resin, a novolak resin or a polyolefin type resin.
In this manner, the resist film can be definitely changed to alkali-refractory by the function of the agent for inhibiting dissolution of the base polymer.
In the second pattern formation method, the agent for inhibiting dissolution of the base polymer preferably has a sulfonic ester represented by any of the following Chemical Formulas 6 through 11: 
wherein R4 and R5 are the same or different groups selected from the group consisting of an alkyl group and an aryl group; 
In this manner, the absorbing property of the resist film against light of a wavelength of a 1 nm through 180 nm band can be definitely decreased.
The second pattern formation method preferably further comprises, between the step of conducting pattern exposure and the step of forming a resist pattern, a step of conducting a heat treatment on the resist film.
In this case, the agent for inhibiting dissolution of the base polymer is preferably a compound that decomposes in the presence of an acid, and the resist material preferably further includes an acid generator for generating an acid through irradiation with the exposing light.
In the first or second pattern formation method, the exposing light is preferably a F2 laser beam or an Ar2 laser beam.